The RFID technology is a generic term descriptive of a data identification method using radio frequencies or identifying media utilizing such data identification method and makes use of an RFID system including an IC tag serving as a data carrier, an IC tag reader/writer and an administrative personal computer. As shown in FIG. 4, the IC tag includes an IC chip, carrying data on merchandise or product information, and a miniature antenna, all embedded in a plastic card. The IC chip contains an ID memory and a communication control circuit. When the IC tag is attached to an object to be identified and information carried thereby is picked up by means of a reader/writer by radio, a traffic control, a merchandise or product control or identification can be accomplished.
By way of example, the Japanese Laid-open Patent Publication No. 2001-56847 discloses an ID tag (IC tag), in which the antenna works satisfactorily even when held in contact with a metallic plate, which can be formed to a relatively small thickness and which does not spoil portability.
However, any machine component carrying an IC tag has not yet been made available in the art, which can be consistently controlled from production to disposal with no possibility of the IC tag being lost.
Under these circumstances, demands have recently increased to enable the traceability of the products, which makes it possible to trace the history, application and whereabouts of products to be identified. When it comes to the quality control of machine components, it is desired that the production history on quality, lot and others at every stage of the manufacturing process from purchase of materials to completion of manufacture (including purchase of materials, forging stage, heat treatment stage, grinding stage and others) can be ascertained or identified on each of the machine components or on a lot-by-lot basis. By way of example, specialty goods such as aircraft bearings are generally examined one by one and, accordingly, it is generally required for the production history of each of those specialty goods to be ascertained. In the case of general goods such as bearings for use with automobiles and industrial machines, the lot-based control is generally practiced and the lot-by-lot sampling inspection procedure is carried out for each lot of products and, accordingly, it is required for the lot-by-lot production history to be ascertained. If the production history is available, not only can the manufacturer easily work around with replacement, identification of a batch or lot of products containing one or more products to be rejected and/or future improvements in the event of occurrence of one or more defective products, but life estimation and a prior replacement in anticipation of a possible occurrence of machine troubles can also be performed easily. In addition, determination of mix-up of analogous goods can also be performed easily.
As a quality control method for clarifying the production history, the method has hitherto been practiced, in which information arising from each stage of the manufacturing process is recorded on a check note or sheet and/or inputted to a database terminal.
On the other hand, in the field of physical distribution management and stock management, the IC tag is increasingly used and, even in the manufacture of components for automobiles, the control from production to disposal using the IC tag has been suggested. See, for example, the Japanese Laid-open Patent Publication No. 2002-169858. Since the IC tag has the ability to record and read out information on a non-contact basis and, since it can have a large storage capacity, a sophisticated control can be expected.
According to the conventionally suggested quality control method using the IC tags, by directly recording various pieces of information about a machine component on the IC tag attached to such machine component, or by consulting the database for the machine component having such identification information while recording identification information about the machine component on the IC tag, material, lot control information and data on various histories, all associated with the machine component can be identified. However, the cause of trouble in the machine component may not be ascertained only with the information on the machine component. By way of example, difference in processing condition at every stage of the manufacturing process often brings about difference in quality and such difference brought about by the difference in the processing condition cannot be often recognized from results of examination. Considering that machine components such as rolling bearings, shaft couplings and ball screws are generally made up of a plurality of elements, even though the results of examination of the machine components are made available, it is virtually difficult to identify the presence or absence of any defect and/or trouble arising from the difference in quality of those elements. In particular, in the case of the machine component including rolling elements of, for example, the rolling bearing, even slight difference in material and precision affects the performance of the resultant machine component and, therefore, the conventionally suggested quality control method using the IC tags is incapable of resolving those problems.
Also, as for the production control, the conventional control method in which data are recorded on a check note or sheet and/or inputted to a terminal device at every stage of the production process requires complicated and time-consuming procedures in accomplishing the recording and/or inputting and, therefore, it is quite difficult for a substantial amount of information to be recorded carefully and meticulously. Specifically, in the case that machine components such as rolling bearings are made up of a plurality of elements and those elements are manufactured on a lot basis throughout the manufacturing process including purchase of material, forging stage, heat treatment stage and grinding stage, the control of those elements at every stage of the manufacturing process is complicated and it is time-consuming to record and input the history information on each of the elements by hand. For this reason, it is difficult to provide the detailed information on history of the machine components, and the control of such information is costly.
In view of the foregoing, the use of the IC tag has been contemplated, but it has been found that the quality control system employed in association with articles of manufactures such as automobiles cannot be applied to the machine components of the kind discussed above. According to the previously mentioned Patent Document (Japanese Laid-open Patent Publication No. 2002-169858), the IC tag is attached to automobiles, which are an object to be controlled, so that information on every stage of the manufacturing process can be recorded. This IC tag is affixed to a frame of each automobile. However, considering that the machine components such as rolling bearings do not make use of any complete element usable as a standard object similar to the automobile frame and that during the manufacturing process those elements are manufactured through forging, heat treatment and the others, no IC tag can be affixed to each machine component itself from the beginning of the manufacturing process. Also, since in the case of the machine components such as rolling bearings, inner races, outer races, rolling elements and other elements are controlled individually at each stage of the manufacturing process including, the purchase of material, a forging stage, a heat treatment stage and a grinding stage, it is difficult to determine how to use the IC tags for the quality control. More specifically, it is difficult to determine which stage of the manufacturing process the IC tag is applied to and/or what portion of each machine component the IC tag should be attached to. Thus, the efficient use of the IC tags is difficult.
Also, there are numerous machines and equipments employing a number of rolling elements as machine components. It is often experienced that the rolling bearings are hardly controlled for lifetime despite of the needs for such control. For example, in the case of the thermal power plant, coals used as fuel are transported with a coal carrier vessel and are then disembarked by a coal lifting crane onto a belt conveyor. The coals transported by the belt conveyor are subsequently piled up on a coal yard and are, when to be consumed, again transported by a belt conveyor towards a boiler. This boiler must be continuously operated along with the belt conveyor to maintain the electric power supply and high fuel efficiency. The belt conveyors make use of hundreds of bearing units of a structure in which bearings are incorporated in tubular rollers.
The belt conveyor must be halted once any abnormality occurs as a result of damages in a major bearing portion used in, for example, a drive unit and, therefore, the major bearing portion must be monitored at all times. To meet this requirement, it is a general practice to use temperature sensors and vibration sensors in those bearings so that they can be monitored at all times as to changes in temperature and vibration. In contrast thereto, since each roller positioned generally intermediate of the length of the belt conveyor and supporting the endless belt makes use of hundreds of bearings, all of those bearings cannot be controlled individually in a manner similar to the major bearing portions of the drive unit and it is not realistic to monitor all of those bearings at all times in the terms of the cost. For this reason, based on a record of the previous replacement date of the bearings, replacement of the bearings is carried out ahead of time to ensure safety before the rated lifetime reaches. In such case, the replacement of the bearings is carried out with the roller incorporating the bearings on a roller-to-roller basis without the belt conveyor being halted.
When it comes to a railway vehicle in which a considerable number of bearings are employed for rotatably supporting wheels, once the railway vehicles start moving, they cannot be brought to a stop along the way in order to transport passengers and/or cargos to the destination. As such, to prevent any trouble from occurring during the operation of the railway vehicles, the bearings are regularly inspected and controlled while the railway vehicle is not operated.
Even with the intermediate rollers used to support the endless belt in the conventional thermal power plant, it is highly possible that the conveyor must be halted depending on the condition of damages once an abnormality occurs in the bearings. The routine bearing replacement can be carried out with proper measures without halting the conveyor solely for replacement purpose. However, the replacement of the bearings while the conveyor is being driven will not be accomplished in the event of an unforeseeable abnormality in the bearings. Even where the early replacement is performed before the rated lifetime, an unforeseeable abnormality in the bearings may occur and no one can know in advancement when it occurs.
On the other hand, in the case of the wheel support bearings used in the railway vehicles, the routine examination of those wheel support bearings is generally carried out while the railway vehicles are not operated as discussed previously. However, in the case of railway vehicles that are operated for a substantial period of time and over a long distance at high speeds, conditions of use of the wheel support bearings are indeed severe. As such, the routine examination is not sufficient to prevent any abnormality in the bearings. As a matter of course, the condition of the wheel support bearings while the railway vehicles are operated cannot be grasped when the railway vehicles are not operated.